Montana Field Guide

Northern Hawk Owl - Surnia ulula

Appropriately named, the Northern Hawk Owl more closely resembles an Accipiter hawk species than an owl, both in morphology and behavior. Dropping from a visible perch on a prominent tree, gliding low over the ground or in high-speed flight, its short-pointed wings and long tail give the appearance of a falcon-like bird (Duncan and Duncan 1998). Following the general reverse sexual size dimorphism found in most owls, the female of this species is larger than the male. Females are generally 37.2 to 44.7 cm in length, while males are approximately 36.0 to 42.4 cm (Duncan and Duncan 1998). Sometimes surpassing males in mass by as much as 17%, females generally weigh 340 grams, while males average approximately 300 grams (Earhart and Johnson 1970, McGillivray 1987). Beneath a fairly flat-topped head and deep v-shaped black and white speckled forehead, the grayish-white facial disc is framed in black. The iris is yellow, the bill is pale yellow to greenish-yellow, and the flesh of the heavily feathered feet is colored a deep slate-gray to black (Duncan and Duncan 1998). The back, wings, and head are brownish-black, spotted and streaked with white, while the white breast and belly are heavily and distinctly barred with brown.

The vocalization of the Northern Hawk Owl is variable and persistent during the breeding season. The display call of the male is a trilling, rolling whistling "ululululululul" lasting up to 14 seconds, while the female's advertising call is shorter and less constant in pitch and rhythm, with a hoarser and shriller quality (Duncan and Duncan 1998). This species is also known to express an alarm or screeching call, a trilling call, a yelping call, a lure call, a soliciting call, a hiss and chitter, and other vocalizations (Duncan and Duncan 1998).

Northern Hawk Owls are easily distinguishable from other species of owls by a long tail and fast, maneuverable flight. The posture of Northern Hawk Owls is more hawk-like than owl-like. Prominent perch selection and hunting by daylight are additional cues that differentiate this species from other owls. The unique shape of this bird, including its moderately wedge-shaped tail, and overall coloration and appearance make it unlikely to be confused with any hawk species (Sibley 2000).

Montana Range

Movement into Montana is sporadic and migration into the state generally reflects irregular movements of individuals and may be in response to local changes in food availability. Observations in the state have occurred in late fall and winter (November-February), as well as late spring and early summer (May and June) (Montana Bird Distribution 2003).

Johnsgard (1986) indicates Northern Hawk Owls prefer post-fire habitat and open muskeg areas, with tall trees or snags for use as hunting perch sites. No other specific information is available on nest site selection in Montana.

Food habits have not been studied in Montana, but research from other studies have revealed that Northern Hawk Owls' diet often is dominated by voles (primary prey in Eurasia), but birds (up to grouse size) may constitute the major part of the diet in winter; juvenile snowshoe hares may be important during certain nesting stages (Rohner et al. 1995, Duncan and Duncan 1998). The main Microtus species preyed upon in North American include Alaska vole (M. miurus), meadow vole (M. pennsylvanicus), tundra vole (M. oeconomus), long-tailed vole (M. longicaudus), and yellow-cheeked vole (M. xanthognathus) (Duncan and Duncan 1998). Other small mammals and bird species that comprise the balance of their diet are numerous and may include shrews, moles, rabbits, hares, squirrels, mice, rats, lemmings, weasels, partridges, doves, woodpeckers, jays, robins, startlings, sparrows, buntings, blackbirds, grackles, and finches (Duncan and Duncan 1998).

Hunting, may occur during the day or night, and is similar to hawk species. The Northern Hawk Owl watches prey from a perch, strikes with a rapid dive, and returns to an elevated perch to consume the food item. The pellets of this owl species are relatively small (up to 7.5 cm long), gray, and coated in mucus (Nero 1995).

Ecological studies have yet to be conducted in the state. However, information from other areas of the species' range shows Northern Hawk Owls tend to occur in the greatest numbers in areas with temporarily high prey populations and may move long distances in response to changes in prey abundance. Population density generally is low (e.g., 4 pairs in 200 square kilometers in Norway; 1 pair per 500 square kilometer in Sweden) (Johnsgard 1988) with a maximum of 3 nests per 100 square kilometers in southwestern Yukon, Canada (Rohner et al. 1995). Home ranges in Europe ranged from 140 to 848 hectares, average 372 hectares (Baekken et al. 1987). In southern Alberta, they establish winter hunting territories (Johngard 1986).

Limited breeding records exist for Montana. The first record of breeding in the western U.S. occurred in Montana in May of 1990, when a brood of 4 recently fledged young were observed in Polebridge. The first nest was confirmed when one was found in West Glacier in 1994 (eight young, seven fledged), and a second nest was recorded in 1995 when a female was photographed at a cavity site (Wright 1996, Montana Bird Distribution 2003). Reproductive studies of Northern Hawk Owls in other areas of their range have found nesting to be in unlined hollows or cavitys.

Northern Hawk Owls produces smooth, slightly glossy eggs that are white, infrequently with a hint of yellow, and are blunt elliptical-oval to elongate-oval in shape (Eckert 1974, Baicich and Harrison 1997). The average egg dimensions are 30.63 to 32.15 mm by 38.64 to 42.48 mm, and weigh an average of 21.6 grams (Mueller 1986). Egg-laying has been reported from late April to mid-June in Alaska and arctic Canada; early April to early June in Alberta (Johnsgard 1986, Duncan and Duncan 1998). Clutch size is up to 13 (mean brood size was 6.3 in Fennoscandia, 3.7 in Yukon, 5.5 in Alaska). Incubation, by the female, starts as soon as the first egg is laid and continues until the last hatches, in total, about 25 to 30 days. Both parents tend the young, which fledge in 25 to 35 days, but may not be fully independent until they are three months old. Survivorship of the later-hatched young is dependent upon food availability. In Europe, a second brood has been reported with the loss of the first clutch of eggs, but this behavior has not been reported in North America (Baicich and Harrison 1997, Duncan and Duncan 1998).

No current management activities in Montana specific to Northern Hawk Owl are documented.